In recent years, along with the rise of a demand for thin-screen TVs, developed have been various types of display techniques, such as liquid crystals, plasma, organic electroluminescence, and field emission. In any one of these displays different in display type, such a transparent electrode is an essential structural element. Further, in addition to such a display, in the fields of touch panels, cellular phones, electronic paper, various solar cells and various electroluminescence control elements, the transparent electrode have become an indispensable technical element.
Conventionally, as such a transparent electrode, mainly used has been an ITO transparent electrode in which an indium-tin complex oxide (ITO) film is formed on a transparent base material, such as glass and a transparent plastic film by a vacuum deposition method or a sputtering method. However, there are the following problems. Since the productivities of the transparent electrodes produced by the vacuum deposition method and the sputtering method are not good, their production costs become high, and since the produced transparent electrodes are inferior in flexibility, they cannot be employed for devices required such flexibility.
For the above problems, proposed is a method of forming a transparent electrode by coating metal oxide particles, such as ITO (for example, refer to Patent Document 1). However, the method has another problem that the transparent electrode cannot obtain sufficient conductivity to function as an electrode. Although the application of baking treatment to the coating layer of metal oxide particles makes it possible to lower a resistance value, the baking treatment cannot be applied to the case that a transparent electrode is formed on a resin base material such as a plastic film.
In order to provide a transparent electrode excellent in productivity, proposed is a method of forming a transparent electrode by coating or printing a coating liquid in which a conductive polymer material represented by π-conjugated polymers is dissolved or dispersed in an appropriate solvent (for example, refer to Patent Document 2). However, as compared with the metal oxide transparent electrode such as the ITO film by the vacuum deposition method, this method has another problem that the transparent electrode has low conductivity and inferior transparency.
Further, disclosed is a technique to employ conductive fibers such as carbon nanotubes (CNT) and metal nanowires, and proposed is an electrode structured such that apart of conductive fibers is fixed with a transparent resin film to a base material and a part of the conductive fibers is protruded from the transparent resin film (for example, refer to Patent Documents 3 and 4). However, the electrode with the above structure has conductivity only on the part where the conductive fibers are protruded. Therefore, the electrode has not a function as a plane electrode. In addition, since the conductive fibers are protruded from the surface, there is a problem that the electrode cannot be applied to technical usage for which the surface smoothness of an electrode is required.